A disadvantage associated with travelling volume pumps is that the effectiveness of the seal between opposed surfaces of the flexible pump tube in a peristaltic pump or between the diaphragm and the pump casing in a travelling wave diaphragm pump, which each form a travelling seal to drive the pumped material in the respective pumps, is related to the mechanical force or pressure applied at the point of sealing. Accordingly, high pumping pressures can only be achieved with high mechanical forces which result in high levels of friction and power consumption.